The upper edge part around the opening of a paper bag is susceptible to injury or breakage by forcible contact with articles as they are placed therein and taken out therefrom. One technique for reinforcing the upper edge part of the paper bag, by providing a turned in collar around the opening thereof which is folded inwardly to build the double wall structure, is disclosed in Japanese Pat. No. 27622/1976.
The outermost surface of the material formed into a conventional paper bag is often subjected to surface processing such as printing or the like and, therefore, the surface of the turned in collar is also subjected to the same processing. Thus, as a result, when a paper sheet that is formed into the paper bag is folded and assembled into the bag-shaped configuration, glueing effected between a glue placing portion and the printed surface portion of the turned in collar involves gluing between two printed surfaces and this has a reduced gluing strength. Accordingly, in the course of repeated usage of the conventional paper bag, peeling at such a portion of the bag tends to occur and breakage tends to occur and spread from that location on the bag. To obviate the foregoing problem it is desirable to locate any printing on the bag away from the surface of the turned in collar so as to increase glueing strength between the glue placing portion and the turned in collar. However, to accomplish this the printing has to be carried out in a complicated manner.